Welded two-piece light alloy piston



May 30, 1939. v R. M. HAZEN ET AL 2,159,939

WELDED TWO-PIECE LIGHT ALLOY PISTON Filed April 19, 1937 s Sheets-Sheet1 wwwa 1939- R. M. HAZEN ET AL 2.159,989

I I WELDED TWO-PIECE LIGHT ALLOY PISTON Filed April 19, 19.37 3Sheets-Sheet 2 ELD 27 HIIIIIII WELD 4.

. 21 fiolla/a'fizgfazeiz & 773071145 5. WZaeft Patented May 30, 19392,159,989 WELDED TWO-PIECE LIGHT ALLOY PISTON Ronald M. Hazen and ThomasS. McCrae, Jr.,

Indianapolis, Ind., assignors to General Motors Corporation, Detroit,Mich., a corporation of Delaware Application April 19, 1937, Serial No.137,656

5 Claims.

This invention relates to pistons and especially to light alloy pistonsfor high speed engines.

It relates particularly to such pistons for use in internal combustionengines.

In modern high speed two-cycle engines, the conditions under which thepistons have to operate are particularly severe. Other things beingequal, the specific output of a two-cycle engine tant to provide pistonswhich are light, but of adequate strength, while capable-of dissipatingeffectively the heat to which they are subjected.

The object of the invention is a strong, light Weight piston, capable ofquickly dissipating the heat to which it is subjected.

Another object of the invention is a piston in which the heat fiow tothe ring belt is limited.

Another object of the invention is a piston which can be oil cooled.

It is-a further object of the invention to achieve the foregoing objectsin a piston which can be simply and cheaply produced.

The above and other objects of the invention will be apparent as thedescription proceeds.

According to the invention, the crown of the piston is supported fromthe piston pin bosses mainly by a circular strut forming an inner wall,spaced from and of greater section than the outer wall of thepistonand-providing an annular insulating air space between the two walls. Thepiston is made in two pieces subsequently fastened together byscrewedand/or welded joints, or the like. One piece forms one part ofthe wall of the annular insulating air space and includes the crown andthe other piece forms the remaining part of the wall of the annularinsulating air space and includes the skirt.

The two piece construction permits of greater control and freedom in thechoice of section and in the provision of suitable cooling fins andinsulating air spaces.

The drawings show several modifications of a piston according to theinvention.

r" In the drawings:

I is a view, partly in elevation and partly in section, of a preferredpiston structure according to the invention.

Fig 2 is a view in elevation of a part of Fig. 1..

Figs. 3 to 8 are views, partly in elevation and partly in section, ofmodifications according to the invention.

Referring now to Figs. 1 and 2.

I is the piston crown and 2 is the piston skirt provided withdiametrically opposite bosses such as 3, having bearings 4 for a pistonpin (not shown).

Between the underside of each boss 3 and the piston skirt is astrengthening rib 5, and the uppermost surface of each of the bosses isa fiat shoulder 6 forming a seating for the circular strut I of thecrown I of the piston.

Immediately above the shoulders 6, the bore of the piston skirt is screwthreaded at I to engage with threads 8 at the lower end of the circularstrut I.

The piston crown I is somewhat mushroom shaped and in the exampleillustrated has a spherical top with a rim 9 which fits closely withinthe bore at the top end I of the piston skirt but with part of the rim 9extending therefrom when the crown with its strut is screwed on to theseatings 6.

The outer diameter of the circular strut of the piston crown between therim and the threads 8, and the bore of the piston skirt between the topI0 and the threads I, are such as to leave an annular space I I betweenthe strut and the skirt when these two parts are assembled.

The annular space extends closer to the outer cylindrical surface of thepiston at points above and below a ring belt area I2 in which grooves I3are provided for conventional packing rings (not shown).

Grooves I 4 with drain holes I5 therefrom to the inside of the pistonare provided at the lower end of the skirt, for scraper'rings (notshown).

Cooling fins I6 are provided within the bore of the skirt 2, at a pointin the annular air space I I above the ring belt area I2.

The inside of the crown I is provided with cir-- cumferential fins IIgiving ample cooling area therein.

The two parts-the piston crown and the piston skirtcan be made of anysuitable light alloy (either forged or cast), and it will be seen that astructure has been provided in which all critical points as well as thecooling fins may be completely machined to any desired tolerance limitsebefore assembly.

manner, after which the joint between the rim, 9

, of the piston crown and the; top end "lot the piston skirt is sealedby welding as indicated in the drawings.

Provision is made for efiective oil cooling of the piston by fitting asheet metal oil retainer H8 in the piston, as shown. It is held inposition by screws I9 in each rib 5 of the piston skirt.

The oil retainer is open at its upper end but forms an annular oil well20 which traps a part of the cooling oil which may be projected in knownmanner from the engine lubricating oil pump up the connecting rod andagainst the underside of the piston crown.

Oil from the well 20 is thrown up against the underside of the pistoncrown and over the cooling fins l1 therein, as the piston decelerates inapproaching its top dead center. Some of the oil projected or thrownagainst the crown is forced through radial holes 2| therein into theannular space H and on to the cooling fins l6 oi. the skirt 2 just abovethe ring belt area l2.

From the annular space H the oil returns through radial holes 22 backinto the oil well 20.

The construction according to Fig. 3 is essentially similar to theconstruction according to Figs. 1 and 2, except that the ring belt area23 is formed as a part of the piston crown 24, and the joint between thecrown 2d and the piston skirt 25 to be sealed by welding is below thering belt area 23, as indicated in the drawings.

The construction according to Fig. 4 is essentially similar to theconstruction according to Fig. 3, except that the strut, (i. e., theinternal wall 26 of the annular air space 21 and the means fortransmitting the loads on the crown of the piston to the piston pin) isformed as part of the piston skirt 28, the screw threaded connectionbetween the piston crown 29 and the piston skirt 28 being towards theuppermost end of the piston, with the piston skirt 28 male threaded andthe piston crown female threaded.

The construction according to Fig. 5 is essentially similar to theconstruction according to Fig. 4, except that the ring belt area 30 isformed as a part of the piston skirt 3|, and the joint between thepiston crown 32 and the piston skirt 3! to be sealed by welding, isabove the ring belt area 30, as indicated in the drawings.

The construction according to Fig. 6 is essentially similar to theconstruction according to Fig. 4, except that the piston skirt is femalethreaded and the piston crown is male threaded.

The construction according to Fig. '7 is essentially similar to theconstruction according to Fig. 5 except that the piston. skirt is femalethreaded and the piston crown is male threaded.

In "the modification according to Fig. 8, the piston pin bosses 33 areintegral with the piston crown 35. The ring belt area 35 is alsointegral with the piston crown 34. The piston skirt 36 is a push fitover the bosses 33 and is welded to the piston crown 34 below the ringbelt area 35, as shown.

While special provision for oil cooling has only been shown inconjunction with the preferred form of the invention shown in Figs. '1and 2 by providing this with an oil retainer I8, and radial holes 2| and22 through'the inner wall of the insulating annular space, it will beappreciated that such means might equally well be applied to theconstruction according to Figs. 3 to 8,

In all the examples illustrated, the heat-flow from the head of thepiston to the ring belt area is restricted by the narrow section ofmetal between these two parts. The circular strut forming the inner wallof the insulating annular air space is sufiiciently large to carry themain gas pressure loads and the heat flow directly on to the piston pinbosses--only a small part of the load and the heat flow beingtransmitted through the outer section of the piston.

Because of the lower temperature of the ring belt area, due to thelessened heat flow to this part, the possibility of piston ringssticking, consequent on carbonization of the lubricating oil at thetemperature which would otherwise exist, is avoided.

Complete machining of ample fin area of minimum section is permitted bythe two piece construction.

Internal oil cooling is desirable in order efiectively to dissipate thegreater heat flow to the inside of the piston, where the heat flowthrough the ring belt area and the piston rings tothe cylinder wall hasbeen reduced to a safe limit in the manner set forth.

We claim:

1. In a piston having a crown, a skirt, piston pin bosses, and a ringbelt area in the outer wall of the piston between the crown and thepiston pin bosses, a strut to support the crown from the piston pinbosses and forming an inner wall spaced from the outer wall of thepiston to provide an enclosed annular insulating air space between thering belt area and the strut forming the inner wall, said inner. wallhaving at all points a greater cross-sectional area than points aboveand below the ring belt area in the outer wall of the piston, wherebyonly small portions of the gas pressure loads and the heat to which thecrown is exposed in an engine cylinder are transmitted to the ring beltarea, and the main portions of the gas pressure loads and the heat floware carried directly through the inner wall to the piston pin bosses,said piston being made in two pieces subsequently fastened together, andhaving a joint in the outer periphery of the piston above the piston pinbosses, one of said pieces forming a part of the wall of the annularinsulating air space and including the crown, and the other pieceforming the remaining part of the wall of the annular insuiating spaceand including the skirt.

2. The combination according to claim 1, in which the ring belt area ispart of the piece including the skirt and the strut is part of the pieceincluding the crown.

3. The combination according to claim 1, in which the ring belt area andthe strut are part of the piece including the crown.

4. The combination according to claim 1, in which, the ring belt area ispart of the piece including the crown, and the strut is part of thepiece including the skirt.

5. The combination according to claim 1, in which the joint in the outerperiphery of the piston above the piston pin bosses is a welded joint,and there is an additional screw threaded connection between the twopieces.

RONALD M. HAZEN. THOMAS s. MCCRAE, JR.

. v CERTIFICATE OF CORRECTION. Patent No. '2, 159,989. M y 3 959- iRONALDM.HAZEN,ETAL. -It is hereby certified that'error appeare in theprinted specification of the above numbered patent requiring correctionae follows: Page 2', second column, line 51, claiml, before the wordspace'! insert air; and that the said Letters Patent should be read withthis correction therein that the same may conform to the record .of thecase in the Patent Office.

'Signed and sealed this'lst day of August, 1959. I

. H Henry van Aredale,

(Seal) 7 Acting Commissioner of Patents--

